Received my Arduino UNO development kit today it came with extra electronic components that will get me started on some simple projects. I bought this on eBay for around $40 AUD and I recommend that you get yours from eBay because if you buy yours locally you are only getting the development board for the same price. The kit came with a breadboard, breadboard wires, some LEDs, switches, sensors, LCD panel, resistors and a USB cable for connecting it my computer.
So you asked what can I do with this thing? You do a lot with this, if you go and search Arduino on the net you see a lot of interesting projects. This development kit is using a ATmega328 microcontroller and on the circuit board has all the components to make it a functional device. So what I did was downloaded the IDE from Adruino web site and compiled an example program and uploaded to the microcontroller and in a few seconds I was able to make an LED (light emitting diode) flash!
You can download the IDE for the Mac OS X, Windows and Linux, and if you are using Ubuntu 11.04 like me you can download the IDE directly from the Ubuntu Software Centre.